1. Technical Field
The present invention relates generally to electric motors, and more particularly relates to rotors in brushless electric motors for use in automotive vehicles.
2. Background Information
A typical brushless motor includes a stator with teeth and coil windings, such as low resistance copper wires, wound on the teeth. During the operation of the motor, a current is passed through the windings to generate an electromagnetic field that interacts with permanent magnets attached to a core of a rotor positioned within the stator. The rotor is in turn coupled to a shaft mounted on a set of bearings so that the electric current passing through the windings is converted to mechanical rotation of the shaft as a result of the interaction between the permanent magnets of the rotor and the electromagnetic field generated by the windings. The shaft commonly provides a physical transfer of the mechanical energy to some other mechanism that may be coupled to the shaft.
In many types of motors, the core of the rotor is laminated steel material and is exposed to ambient conditions. As such, fluid is able to seep through the laminates into the core and thus corrode the core, thereby compromising the structural integrity of the core. Furthermore, since the magnets are usually secured to the core with a retainer mechanism, a post balancing operation may be required to balance the rotor after it has been assembled.
From the above, it is seen that there exists a need for a rotor that has reduced susceptibility to corrosion and that eliminates post balancing requirements.
In overcoming the above mentioned and other drawbacks, the present invention provides a rotor for an electromagnetic motor with a plastic bonded magnet. The plastic bonded magnet is injection molded to a core, which in turn is affixed to a shaft. The percentage of magnetic material bonded to the plastic in the rotor can be tailored to the flux requirements of the motor.
In one embodiment, a rotor assembly for a brushless motor includes a core circumferentially affixed about a longitudinal surface of a shaft and a rotor magnet injection molded about the core. The magnet covers the entire outer surface of the core. By covering the entire outer surface of the core, the magnet seals the core within the magnet to prevent exposure of the core to ambient conditions, particularly corrosive fluids. As is typical for rotor construction, the rotor magnet has a plurality of portions of alternating magnetic polarity. In the present construction, these portions are formed of a plastic mixed with neodymium-iron-boron.
The foregoing discussion has been provided only by way of introduction. Nothing in this section should be taken as a limitation on the following claims, which define the scope of the invention.